1. Field of the Invention
The invention relates to an electric machine having a housing, a stator, disposed in said housing, with indirectly cooled stator winding conductors disposed in grooves on the inside circumference, and a rotor, the laminated body of the stator being constructed of individual laminated subassemblies spaced from each other by spacing bridges and the intermediate cavities between two successive laminated subassemblies forming radially extending cooling slits, and the cooling slits connecting annular air-gap cavities at the inside circumference of the laminated stator assembly to chambers which are situated between the outside circumference of the laminated stator body and the housing and which chambers comprise cold-gas chambers, from which cold cooling gas is forced into associated first air-gap cavities, and comprise hot-gas chambers into which heated cooling gas flows from second air-gap cavities in a radially outwards direction, there being provided at least at one end of the machine, preferably at both ends of the machine, cooling-gas impellors and cooling-gas guidance devices which supply the cooling gas, cooled by heat exchangers, as cold gas to the cold-gas chambers and extract the heated cooling gas from the hot-gas chambers again.
A gas-cooled electric machine with these features is known, for example, from the European Patent Application No. 0172397 or from the German Offenlegungsschrift No. 3,444,189.
2. Description of the Prior Art
The principle of the so-called indirect cooling system is to transfer the losses produced in the stator winding rods to the cooling medium (hydrogen or air). The main heat flow takes place under these circumstances from the rod copper via the insulation to the tooth region of the laminated stator body. From the stator teeth, the heat is transferred to the cooling medium.
The limits imposed on the heating up are fixed under these circumstances by the temperature sensitivity of the insulation and, in addition, by appropriate maximum temperatures which are laid down in national and international standards by various insulation categories.
As a consequence of the relatively large temperature difference between the stator copper embedded in the insulation and the outside layer of the insulation, the maximum output of an indirectly gas-cooled turbo generator is limited by a classical cooling principle.
There has therefore been no lack of proposals for improving the cooling, these efforts being concentrated mainly on intensifying the cooling in the central region of the machine.
Thus, the European patent application mentioned in the introduction describes a gas-cooled electric machine in which cooling gas is supplied and removed through cooling slits combined in groups. In one group, cold cooling gas flows from the core back to the air gap of the machine, while in the other group, heated cooling gas flows from the air gap of the machine to the stator back. In order to prevent an application of already heated cooling gas to the winding conductors, the winding conductors are partitioned off in the cooling slits of the second group and are cooled by axial channels in the tooth head which are open with respect to the winding conductors and through which fresh gas flows. This makes a substantial equalization of the temperature level in the longitudinal direction of the active section possible.
In the case of the gas-cooled machine known from the German Offenlegungsschrift No. 3,444,189, to improve the heat transfer and utilize the cooling-gas flow, the teeth of the laminated stator body are provided with cooling channels in the teeth, which channels are in communication with radial cooling-gas slits, and in particular, cold-gas slits and hot-gas slits. In the axial region of the cold-gas chambers, radial/axial cooling paths are formed by varying punchings of laminated layers which are adjacent to each other, the punchings overlapping at least radially. The cooling paths debouch into the air gap of the machine via cooling-gas outlet slits. A cold-gas circuit is superimposed on the laminated subassemblies disposed in the axial region of the hot-gas chambers. For this purpose, axial overflow channels and radial additional slits are provided. The latter are disposed in each case fairly centrally between the radial hot-gas slits and have a smaller axial width than the latter.
Both known measures require comparatively large interventions in the structure and the design of the laminated stator body and are therefore expensive.